1. Field of the Invention
The present invention relates to sailboats and particularly to an improved lifting-sail rig and method for multihulls and wide beam monohulls with a simple, effective, seaworthy apparatus for the control of heeling with the capability for completely canceling the overturning moment.
2. Description of the Prior Art
The conventional stayed, fixed mast rig used with a weighted keel, monohull sailboat has proven successful in providing the most stable mode of sailing in heavy winds and seas, with shortened sail or reefing to avoid capsizing. The weighted ballast on a keel has proven successful in providing operating stability, but the added weight, keel surface area, and the heeled hull shape increases water drag. Smaller conventionally rigged, centerboard sailboats utilize crew weight to windward with sail easing and sail reefing, to balance the overturning moment created by high wind forces. Control of all conventional sailboats is limited by the need for ultimately xe2x80x9cluffingxe2x80x9d, easing the sail outboard, or reefing for reducing the effective sail area to maintain stability against capsizing. Heeling results in loss of efficiency as a result of the added downward sail force or xe2x80x9cweightxe2x80x9d, which greatly increases hydrodynamic drag, and a large loss in forward aerodynamic driving force. At small angles of heel a multihull having a wide beam and narrow hulls with reduced inertial drag, has proven more stable than a wide beam monohull. However, like any non-ballasted, lightweight sailboat, a multihull tends to capsize when it reaches negative stability in a heavy wind, usually at heel angles greater than about 50 degrees. The maximum design value of the its achieved righting moment limits a sailboat""s xe2x80x9cpower to carry sailxe2x80x9d, whereas increased speed is directly related to the ability to carry a larger sail area where conventional sail rigs are deficient.
The relatively small xe2x80x9cwindsurferxe2x80x9d is the only commercially successful seaworthy lifting-sail craft that completely balances the overturning moment with crew weight. The windsurfer is a one person, aerodynamically efficient, simple, high-speed sailboard. U.S. Pat. No. 3,487,800 to Schweitzer and Drake discloses this lightweight windsurfer with a simple, base pivoting carbon fiber mast, integral with an aerodynamically shaped leading sail edge. The windsurfer sail is manually controlled by the operator, who maneuvers the sailboard by tilting the sail with an attached wishbone boom, fore and aft for steering, and outboard to windward for lifting and balance. The windsurfer operator can skillfully exercise control without capsizing in strong winds and turbulent seas. The planing windsurfer is the only production sailboat that has achieved a world speed record of 45 knots, even though in a 50 knot wind. Depending on the strength of the wind, by tilting the sail rig to windward, the operator can obtain near xe2x80x9clift-offxe2x80x9d conditions where hydrodynamic drag approaches zero. A skilled operator can actually lift the sailboard out of the water briefly and return safely to the water surface. However, the upside growth of windsurfing has been limited by the fact that relatively strong wind conditions are required to optimize windsurfer sailing speed. For high speed in light to moderate winds, a large sail area is required in excess of about 10 square meters. But, only those strong sailors over 6 feet tall can generally realize the strength with enough moment arm to handle these larger sail areas with ease and effectiveness in a strong wind. Limited by the height and strength of the average human operator, the most utilized sail area is actually reduced to about 5 or 6 square meters. Consequently, the windsurfer with its operator supported tilting mast and lifting-sail has a ratio of maximum sail area to total weight ratio much lower than can be achieved with conventional monohulls and multihulls having conventional mounted fixed stayed, or carbon fiber masts.
One of the most rapidly growing high performance sailboat categories is multihulls. Catamarans or trimarans can carry a large sail area, but are more difficult to control than the simpler windsurfer. Multihulls have a tendency in a strong wind to heel to an angle of negative stability, pitch pole, or capsize. However, stayed fixed mast sailboats have proven to have a suitable platform for practical innovations that enhance performance and stability. Conventional vertical sailing rigs may have simple fore and aft stays and side stays or shrouds that substantially support the fixed mast in pitch, roll, and yaw. Alternating pitching forces with the high stress concentrations do not cause premature failure of conventional rigging, and is adequately strong and seaworthy to withstanding the high cyclical stresses from the sail pitching moment in rough seas.
An experimental sailboat named Yellow Pages Endeavor, with an efficient 300 square foot airfoil supported by three stays attached to three short planing hulls asymmetrically arranged, attained the worlds speed record in October 1993 of over 46.5 knots or 53.6 mph in only an 18 knot breeze in relatively smooth water. Furthermore, the iceboat with a stayed mast-sail rig is a good example of the highest speed potential of over 80 knots with extremely low drag on ice.
Prior art lifting-sail arrangements including those that physically mount and rotate the sail about a fixed mast, have proven to be overly complex and difficult to operate. Furthermore, they are difficult to tack or change direction, and they do not have the capability to fully counteract heeling for a complete righting moment. A swing sail rig disclosed in U.S. Pat. No. 4,799,443 to Vogel, comprises a sail luff boom mounted on a single multi-hinge fitting at a pivot point above the sail center of effort with the upper region of the luff boom attached to the top of a short fixed mast. The single multi-hinge fitting connects the luff boom to the mast for both supporting and articulating the swing sail rig. The small multi-hinge mast fitting attached at the mast head allows the sail to rotate vertically around the mast, while rotating about the axis of the luff boom for altering the angle of attack of the sail to the relative wind direction. At the same time the sail can swing or tilt outboard to some extent under the driving force of the wind. Difficulty in maneuvering the luff boom, fixed only to the single mast support fitting results in mechanical interference with the mast. Also, the fixed mast placed in front of the luff boom in close proximity to the swing sail, results in aerodynamic sail interference with increased drag. When sailing to windward, the most critical and difficult point of sailing, the single multi-hinge fitting would tend to have difficulty enduring the very large torsional stresses from the sail forward driving force, and the large pitching moment between the sail center of effort and the multi-hinge fitting, particularly as the sail tends to twist or pitch aft. The strength may be improved as disclosed in U.S. Pat. No. 6,189,472 to Duncan by providing support of the swing sail with an additional swing boom to the boat deck. However, the short swing boom length required to adequately strengthen the rig, limits the outboard swing and the subsequent achievable righting moment. An early U.S. Pat. No. 1,670,936 to McIntyre discloses an early lifting-sail and mast apparatus allowing the sail center of effort to swing outboard to the lee side of the mast, and to pass thru the keel center of lateral resistance for realizing a complete righting moment for all points of sailing. The lee outboard support for the complex rotating lifting-sail apparatus includes a sprit-boom mechanism coupled to the fixed mast, but not substantially supported against pitch, roll, and yaw.
Consequently, improved simpler, more substantial and reliable fixed mast lifting-sail rig and method is needed for controlling heeling with the capability for a complete righting moment under high wind operating conditions. The simple lifting-sail rig apparatus and method of the present invention, with effective operator control, is more aerodynamically efficient, being positioned forward of a conventional fixed mast rigging with a mast-sprit. A preferred embodiment utilizes a low drag carbon fiber, simplified mast rig with the improved high aspect ratio lifting-airfoil or lifting-sail, that operates automatically with rapid response in the same simple, natural way of a conventional sail. To achieve the foregoing and other objects in accordance with the purpose of the present invention, according to one aspect of these novel improvements, various related versions of the preferred lifting-sail rig and method are disclosed.
The improved airfoil or lifting-sail rig for driving or propelling a sailboat, may comprise preferably, a simple carbon fiber aft positioned mast with a lower vertical portion and a short, horizontal mast-sprit upper portion projecting forward from the top of the vertical mast portion for supporting the lifting-sail or lifting-airfoil. An aerodynamic shaped luff-spar is attached to the leading edge of the sail or integral with the airfoil leading edge design. A universal head coupling connects the head end of the luff-spar to the middle region of the mast-sprit portion for unrestricted upward tilting or lifting of the sail or airfoil at the mast-sprit to produce a complete righting moment. Support of the luff-spar against fore and aft pitching is controlled, particularly when sailing to windward by a substantial guy wire that may be a rigid rod or fore-spar. The guy wire is connected between a luff-spar coupling that may be located in the mid region of the luff-spar and a coupling at the forward end of the mast-sprit. This simple method of tilting the airfoil or sail to adjust the heel control is about the axis defined by the mast sprit. The angle of attack of the lifting-sail is altered by rotating the luff-spar about an axis defined by a line between the universal head coupling and the luff-spar coupling.
An alternative lifting-sail rig embodiment may comprise a stayed mast with spreaders that prevent buckling of the mast and distortion of the rig during the pitching, (torsional) yawing, and rolling motion of the sailboat. Again a short, horizontal mast-sprit portion projects forward from the top region of the aft mast for supporting an efficient lifting-sail.
The efficient lifting-sail apparatus is easily controlled by the operator with the aid of the wind naturally forcing the sail into the desired attitude of lift angle and angle of attack in the same manner as a conventional sail. The sail or airfoil may be operated by two sheets, one to control horizontal (outward lifting) tilt preferably at the tack, and the other to control the upper edge of the sail or airfoil may include a top boom with a main sheet leading from the top region of the mast for controlling the angle of attack by the operator. Alternatively, a main sheet leading from the clew may be used to control rotation of the sail angle of attack to the relative wind direction. The balancing lifting force of the sail may un-weight the sailboat and reduce the hydrodynamic drag to a near zero xe2x80x9clift-offxe2x80x9d state, or a complete righting moment may be achieved by the unrestricted upward tilting of the sail or airfoil as desired by the operator.
The objective is to increase the improved lifting-sail rig apparatus high wind speed potential beyond conventional sailboats, with ease of handling, safety, durability, and control in heavy winds and seas. An improved aerodynamically efficient and reliable sailboat, can achieve higher speeds with stability and control over capsizing on all points sailing.,
A primary objective of this present invention is to provide an improved lifting-sail rig high speed sailboat, that achieves stability and control over capsizing on all points sailing, with ease of handling in heavy winds and seas.
Another objective is to provide a simple, efficient lifting-sail rig capable of easily and naturally inclining upward to a high lift position, for optimum control of the heeling force with the capability for complete balance of the overturning moment.
Another objective is to provide a simple, efficient lifting-sail rig capable of an unrestricted upward lifting-sail orientation for the maximum lift position of the sail rig in very strong winds, with the lifting resultant passing directly through the keel center of lateral resistance for complete balance of the overturning moment.
Another objective is to achieve a low aerodynamic drag lifting-sail stayed mast and rigging with good sea keeping ability and superior structural strength.
Another objective is to achieve a low aerodynamic drag lifting-sail simple carbon fiber mast and rigging with good sea keeping ability and superior structural strength.
Another objective is to achieve a low aerodynamic drag lifting-sail stayed mast and rigging with good sea keeping ability and superior structural strength.
Another objective of this present invention is to control the lifting-sail rig with the wind naturally forcing the sail into the desired attitude of lift angle and angle of attack.
Still another objective of this invention is to achieve a larger sail coefficient of lift, higher aspect ratio, more efficient sails or airfoils to achieve a higher overall driving force.
Another objective is to utilize the improved stability of the lifting-sail result afforded by the xe2x80x9cwindsurferxe2x80x9d with the attendant, un-weighted, minimum area hull planing capability with reduced hull drag.
Another objective is to achieve an apparatus with maximum spacing between the sail center of effort and the keel center of lateral resistance to permit the angle of the lifting-sail to be as near vertical as feasible with the overturning moment completely balanced.
Another objective is to provide a method for complete balance of the overturning moment of a lifting-sail rig multihull with only one hull in the water for reduced drag, by causing the lifting-sail to heel the catamaran to windward, thereby moving the center of lateral resistance to the keel of the windward hull.
Another objective is to provide complete balance of the overturning moment of a lifting-sail rig trimaran, moving the center of lateral resistance to the fin of the windward ama, or outrigger of the trimaran, furthest to windward from the lifting rig center of effort.
Another objective is to provide a low profile drag airfoil or sail rig for a safe xe2x80x9chove toxe2x80x9d, or non driving condition, whereby the sail rig may be orientated by the wind force into near horizontal, or vertical xe2x80x9cluffingxe2x80x9d position facing into the wind.
Another objective is to provide a safe xe2x80x9chove toxe2x80x9d, or non-driving condition, whereby a lifting sail or rigid airfoil may be lowered into a rest or nesting position on the deck for mooring or docking the sailboat.
Another objective of this invention is to permit the use of a delta shaped sail or airfoil with an efficient tapered, aerodynamic shape to provide a higher coefficient of lift, lower center of effort, lifting-sail rig with ease of handling and good sea keeping ability, which may be light weight and inflatable similar to conventional delta shaped hang-gliders and kites.
Another objective is to provide dual airfoils, as a fixed bi-plane, or in tandem that may be rotated into the advantageous, efficient xe2x80x9csafe leeward positionxe2x80x9d configuration, to lower the center of effort and increase the righting moment with minimum aerodynamic drag.
Another objective is to maximize the hull speed in relatively calm seas, with a plurality of small surface area, short planing pods having reduced hydrodynamic drag.
Another objective is a craft comprising a least three, but preferably four widely spaced of short planing pods that may be interconnected in a symmetrical array, with small hydrofoils for control and lift.
Another objective is to provide an adequate space between short planing hulls for a crew cockpit, cabin or living quarters without interference from the lifting-sail rig.
Another objective is to maximize the hull speed in ocean going windward performance, with small surface area, very long narrow semi-circular hulls having low wave drag and low inertial drag.
Another objective is to achieve ultimate safety and heavy weather multihull operation, sea-keeping ability, and a built in life saving provision, particularly for trimarans, catamarans, or similar multihull craft adapted with at least one self righting, detachable xe2x80x9clife supportxe2x80x9d elevated capsule or large crew pod with a self-sufficient spaceship-like quality.